When a morphologic region of interest of a bone has to be visualized in an X-ray image including said bone, the orientation of the bone in the image may not be optimal in view of assessing the whole extent of the region of interest.
Indeed, despite the fact that the radiologist or technician attempts to position the bone in an optimal position with regard to the X-ray orientation, the relative bone and X-ray orientation may be such that the region of interest is at least partially masked by another part of the bone and thus hinders a correct assessment of the bone morphology.
This issue arises in particular in—but not limited to—the assessment of femoro-acetabular impingement (FAI).
Femoroacetabular impingement is characterized by pathologic bony lesions on the acetabulum (“pincer” lesion) and/or femoral head-neck junction (“cam” lesion).
These bony lesions can cause intra and extra-articular collisions within the hip joint during certain dynamic activities, resulting in structural damage to the cartilage and labrum of the hip joint.
Bony lesions associated with FAI are typically treated with open or arthroscopic resection of the pathologic bony lesion.
The current standard of care relies on standard 2D X-ray views (such as AP (antero-posterior) pelvis, Dunn lateral, cross-leg lateral) and 3D medical imaging modalities (in particular CT (Computed Tomography) and MRI (Magnetic Resonance Imaging)) to perform a pre-operative assessment of the extent of the bony lesion associated to FAI and create a surgical resection plan.
When performing a pre-operative radiographic assessment, multiple 2D X-ray views are required in different hip joint positions and different X-ray orientation in an attempt to characterize the 3D nature of the bony lesion.
Up to five X-rays are usually obtained for diagnosis and surgical planning.
These X-rays are often repeated due to errors in patient positioning during image acquisition, which result in increasing the radiation exposure for the patient and for medical staff.
Besides, the positions of the bony lesions can vary substantially from patient to patient.
As a result, due to the 2D nature of X-ray projection imaging, the radiographic views often fail to capture the full extent of the bony lesion.
This problem has been partially addressed with the increased utilization of pre-operative 3D medical imaging (CT and/or MRI) for more comprehensive visualization and measurement of bony lesions associated with FAI.
Measurements are often made in multiple planes from these 3D images and these images are sometimes segmented to create 3D renderings of the joint morphology.
Combining the information derived from X-rays, MRI and/or CT, the surgeon is usually able to adequately appreciate the 3D nature of the bony pathology and create a pre-surgical resection plan.
However, while the move to 3D imaging has improved the ability to develop a pre-operative resection plan, intra-operative assessment of the surgical resection of the bony lesion still relies primarily on 2D X-ray imaging, using C-arm fluoroscopy.
Hence, the surgeon often spends a significant amount of operative time moving the hip joint through a range of motion in order to determine the radiographic view for optimal visualization of the bony lesion.
It is indeed difficult for the surgeon to translate the pre-operative morphologic assessment (either 2D or 3D) into the specific hip joint position and/or X-ray orientation required for optimal visualization of the bony lesion.
Alternatively, some surgeons may not perform a thorough intra-operative radiographic assessment, thereby often missing the full extent of the bony deformity.
Taken together, the lack of optimized intra-operative radiographic views of the bony deformity leads to increased operating time, increased radiation exposure for the patient and medical staff and/or incomplete resection of the bony lesion.